1. Field of the Invention
This invention is related in general to the field of inductors, in particular, to transformers, inductors, and coils which are mounted on printed circuit boards or the like.
2. Description of the Related Art
Foil windings are becoming usual in a variety of electrical inductance applications. They are used in coils, inductors, and transformers of many varieties and applications. Their uses range from children's toys, to household appliances, to high technology and aerospace applications.
While the advantages of foil windings are acknowledged, there continues to be some problems associated with the use of foil windings and similar winding materials such as parallel bonded magnet wire. One problem is connecting the foil winding to round wires. Round wires are typically used to conduct electric current to or from the foil winding. The cross section of the round wire is usually significantly less than the cross section of the foil. The result is local heating at the connection point, loss of energy, and higher failure rate.
Another problem is wrapping foil windings on a bobbin. Prior art bobbins (see FIG. 1) are useful when the windings comprise many layers of fine wire. However, as the width of the wire increases, the bobbin flanges cause the exits from early windings to interfere with later windings. This decreases the number of turns which the bobbin can accommodate on a single layer. This interference increases with wire size. The interference is even worse for parallel bonded magnet windings and even more serious for foil windings. For switching power supplies, increases in power levels and increases in switching frequency tend to require a decrease in the number of turns in a winding and an increase in the width of a winding turn. Under these conditions the interference caused by the exits from various windings becomes even more serious.
The prior art has attempted to solve these bobbin problems by cutting deep slots in the bobbin flanges to allow exits of early windings, however, increases in the width of the windings has required ever wider slots in the flanges.
Clearly there exists the need for an improved coil configuration which solves the problems associated with connecting a round wire to a foil winding, reduces interference from exits of windings, reduces energy loss, reduces local heating, and improves reliability.